1. Field of the Invention
The present invention relates to an information display device, and particularly to an information display device for use in an image display apparatus that is used with being placed in front of an observer's eyes.
2. Description of the Prior Art
Conventionally, several image display apparatuses that are used in front of an observer's eyes with being mounted on an observer's head or face, or being held with hands are known, and they are manufactured for use in the field of virtual reality and in the so-called personal theaters. In recent years, an image display apparatus serving as a display for a wearable computer has been studied.
As a detailed construction, for example, Japanese Laid-Open Patent Application No. H7-333551 discloses a construction, that is, in an observation optical system that directs light emitted from an original image to an observer's eyeballs, the light is totally reflected from a curved surface in the direction away from the eyeballs, and the totally reflected light is reflected on reflecting surfaces, preferably, on the reflecting surfaces having different optical powers resulting from the difference in their azimuth angles, and then the light is transmitted through the curved surface and directed to the eyeballs.
Japanese Laid-Open Patent Application No. H9-197336 discloses another construction, that is, in an image display apparatus composed of an image display element for displaying images and an eyepiece optical system (ocular optical system) for directing the image formed on the image display element to an observer's eyeballs without achieving image formation in an optical path, the eyepiece optical system has at least three surfaces, and the light exiting from the image display element is reflected at least three times on the at least three surfaces and reaches the observer's eyeballs, and at least one of the three reflecting surfaces is a concave mirror concave to the observer's eyeballs side.
U.S. Pat. No. 5,790,311 discloses another construction comprising at least three juxtaposed optical surfaces, characterized in that at least two optical surfaces of these three optical surfaces are defined by curved surfaces concave to a pupil position side of the optics system and at least four reflections occur between the curved surfaces.
U.S. Pat. No. 5,699,194 discloses another construction that includes an image display device for displaying an image, and an ocular optical system for projecting the image formed by the image display device and for leading the projected image to an observer's eyeballs. In this image display apparatus, the ocular optical system is arranged such that light rays emitted from the image display device are reflected three or higher odd-numbered times before reaching the observer's eyeball, and that a surface of the ocular optical system that is disposed immediately in front of the observer's eyeball is a reflecting surface which internally reflects the light rays, and through which the light rays exit from the ocular optical system.
Japanese Laid-Open Patent Application No. H10-307263 discloses another construction in which a prism optical element formed of a plurality of surfaces with a medium having a refractive index larger than 1 in between includes a first to a fourth surface. The first surface has both a transmitting action that permits light to enter the inside of the prism optical element or to exit from the inside of the prism optical element, and an internally reflecting action in the prism optical element. The second surface is so arranged as to face the first surface with the medium in between, and has an internally reflecting action in the prism optical element. The third surface is so arranged as to be substantially adjacent to the second surface and as to face the first surface with the medium in between, and has an internally reflecting action in the prism optical element. And the fourth surface has a transmitting action that, when the first surface has an action of permitting light to enter the inside of the prism optical element, permits light to exit from the inside of the prism optical element, and that, when the first surface has an action of permitting light to exit from the inside of the prism optical element, permits light to enter the inside of the prism optical element. And this construction fulfills a range defined by a predetermined condition.
U.S. Pat. No. 6,094,241 discloses another construction that has a display optical system for guiding a light beam from a display means displaying image information to an eyeball of an observer, and an image-pickup optical system for focusing a light beam from the outside on an image-pickup device. This construction includes an optical path separating means provided in an optical path that is arranged to substantially align an eyeball optical axis of a light beam incident from the display optical system to the eyeball of the observer or a virtual eyeball optical axis as an extension of the eyeball optical axis with an outside optical axis of a light beam incident from the outside of the image-pickup optical system, and a shield means for preventing the light beam from the display means from entering the image pickup device of the image-pickup optical system.
Japanese Laid-Open Patent Application No. H5-346508 discloses another construction including a hologram lens by which a light beam corresponding to image information transmitted from an image display device is diffracted in a predetermined direction, and the image information and other image information are spatially superimposed for being observed in an identical field of view. Here, the hologram lens is of an off-axial type composed of a plurality of elemental holograms having the same numerical aperture.
Japanese Laid-Open Patent Application No. H9-185009 discloses another construction that includes an image display means arranged on a predetermined part of spectacles such as spectacle lenses or spectacle frames for outputting a displayed image toward the spectacle lenses, and a see-through means that enables an observer to observe, through the spectacle lenses, the displayed image and the outside at the same time.
Japanese Laid-Open Patent Application No. H10-319343 discloses another construction including an image display means for emitting image display light, a bundle of optical fibers that reduces the image display light transmitted from the image display means and emits it via the end of an exiting surface, and an in-front-of-eyes optical means that directs the image display light exiting from the end of the exiting surface of the bundle of optical fibers to an observer's eyes by diffracting or reflecting it in order to make the observer observe a virtual image formed in accordance with the image display light.
U.S. Pat. No. 5,453,877 discloses another construction including, in series: a generator or source of light images to provide a light radiation, a collimation objective or collimator to collimate the radiation, a combiner comprising a confocal assembly with a first parabolic mirror, a second parabolic mirror, and a transparent plate. The first mirror is reflective to reflect the collimated radiation towards the second mirror, and the second mirror is partially transparent to enable, simultaneously, the transmission by reflection, towards an observer, of the radiation received from the first mirror, and the transmission by transparency, towards the observer, of an external radiation. The transparent plate have two ends being formed, respectively, by the two parabolic mirrors, and a first and a second surface thereof are parallel. And an optical path of the collimated radiation between the objective and the observer includes, substantially, a first crossing of one of the two parallel faces, a reflection on the first mirror, several total reflection on the parallel faces, a reflection on the second mirror and a second crossing of one of the two parallel faces, wherein the plate is formed by several elements, each of the two parallel faces being formed by a surface for each element, and the surfaces being arranged so as to constitute a folded version of the system.
U.S. Pat. No. 6,008,778 discloses another construction including an ocular optical system that leads an image formed by two-dimensional display means to an eyeball of an observer to thereby project the image as an enlarged virtual image. The two-dimensional display means has a first two-dimensional display device and a second two-dimensional display device. An ocular optical system includes a first surface having both reflecting and transmitting actions, a second surface having at least reflecting action, and a third surface having at least reflecting action. The first surface is disposed to face an observer's eyeball. The second surface is disposed to face the first surface. The third surface is disposed to face the first surface in a side-by-side relation to the second surface. Thus, images displayed by the first and second two-dimensional display devices are led to the observer's eyeball.
In the construction disclosed in Japanese Laid-Open Patent Application No. H7-333551 previously described, an observation optical system is composed of a prism using concave reflecting surfaces including a light-beam-selective surface for selectively performing total reflection or transmission in accordance with the incident angle of a light beam; however, it is so designed that, in the prism, reflection occurs with geometrical regular-reflection-angles, and this is disadvantageous in making the optical system thinner. In addition, in the prism, there is no portion where reflection occurs between the surfaces facing each other, in other words, the prism does not have a light-beam-guide portion, and this makes the prism thicker. Furthermore, this apparatus is provided with a so-called see-through function for simultaneously observing a displayed image and an external image; however, a combiner thereof has a semi-transmissive surface, and therefore the light amount of the external image and the displayed image is reduced to as a low level of half of the original amounts. In this construction, prisms for correcting the distortion of a transmitted image delivered from the outside are connected on a curved surface, and this makes it difficult to manufacture this apparatus.
In the constructions disclosed in Japanese Laid-Open Patent Application No. H9-197336, U.S. Pat. No. 5,790,311, and U.S. Pat. No. 5,699,194 previously described, a prism has surfaces facing each other and free-form surfaces partly including a light-beam-selective surface that selectively performs total reflection or transmission in accordance with the incident angle of a light beam. Here, a light beam is directed to a concave reflecting surface through reflection occurring between the surfaces facing each other. However, the same as the construction mentioned above, they are so designed that reflection occurs in the prisms with geometrical regular-reflection-angles, and this is disadvantageous in making the optical system thinner.
In the constructions disclosed in Japanese Laid-Open Patent Application No. H10-307263, and U.S. Pat. No. 6,094,241 described previously, the same as the construction mentioned above, a prism has surfaces facing each other and free-form surfaces partly including a light-beam-selective surface that selectively performs total reflection or transmission in accordance with the incident angle of a light beam. It is so designed that a light beam is directed to a concave reflecting surface through reflection occurring between the surfaces facing each other. And these constructions makes it possible to achieve see-through observation of a transmitted image delivered from the outside. However, the same as the construction previously described, it is so designed that, in the prism, reflection occurs with geometrical regular-reflection-angles, and this is disadvantageous in making the optical system thinner.
Especially, in the construction disclosed in Japanese Laid-Open Patent Application No. H10-307263, see-through observation of a transmitted image delivered from the outside is achieved out of an image display area, and therefore it is impossible to secure a wide external observed area. This application includes a practical example in which the outside is observed while withdrawing a prism; however, this requires a movable portion, and therefore it makes the construction complicated. In the construction disclosed in U.S. Pat. No. 6,094,241, a half mirror is used as a combiner, and therefore the transmitted image delivered from the outside becomes dark.
Japanese Laid-Open Patent Application Nos. H5-346508, H9-185009, and H10-319343 disclose constructions in which, as a combiner, a reflection-type hologram lens is used; however, their optical systems are not so deigned as to fold light beams from the displayed image and are thus less compact. In addition, in order to separate the displaying light beams from the observing light beams, a decentering amount of the hologram combiner is increased and aberrations caused by decentering occur (hereinafter, aberrations caused by decentering will be referred to as “decentering aberrations”), and therefore it is impossible to obtain a favorable displayed image. Especially, the construction disclosed in Japanese Laid-Open Patent Application No. H9-185009 has a large decentering amount, and therefore it is substantially impossible to obtain a wide angle of view.
In the construction disclosed in U.S. Pat. No. 5,453,877, to a prism using concave reflecting surfaces including a light-beam-selective surface that selectively performs total reflection or transmission in accordance with the incidental angle of a light beam, a prism for correcting distortion of a transmitted image delivered from the outside is attached. Here, as a display optical system, an image-reformation optical system is used, and therefore this is less compact. In addition, an eyepiece function of the display optical system is achieved by reflection on the concave reflecting surface, and a hologram functions only as a combiner and does not have any optical power for such as condensing light. Therefore, reflection occurring in the prism (or a plate in a practical example) has geometrical regular-reflection-angles, and this is disadvantageous in making the optical system thinner. Furthermore, it is difficult to form a hologram on a concave reflecting surface.
In the construction disclosed in U.S. Pat. No. 6,008,778 previously described, because of its optical construction, an image light beam passes a half-mirror twice, and therefore its light amount is reduced to less than one fourth of the original amount, and this makes the obtained image dark. In addition, in a prism, there is no portion where reflection occurs between the surfaces facing each other, in other words, there is no light-beam-guide portion, and this makes the prism thicker. Furthermore, it is so designed that a display element is arranged in front of an observer, and therefore it is impossible to provide this apparatus with a see-through function which enables the observer observe a displayed image and an external image at the same time.